1. Field of the Invention
The present invention relates to a hydraulic shock absorber which includes additional pneumatic means for improving the secondary performance of the shock absorber.
2. Description of the Art
It is known that a hydraulic shock absorber contains oil sealed therein for dampening applied forces. A shock absorber construction is disclosed in U.S. Pat. No. 3,770,258 which includes a cap covering a rubber mount by which the shock absorber is supported on a vehicle body, the cap providing a closed space which is filled with oil from the shock absorber proper. The space defined in part by the rubber mount is variable in volume as the rubber mount is resiliently deformed. Such volume variation of the space is functionally combined with the hydraulic pressure within the space to provide a shock-absorbing function of the shock absorber. The primary performance of the shock absorber resides in the interaction between the shock absorber and a wheel on which the shock absorber acts, and a secondary performance of the shock absorber resides in the interaction between the shock absorber and a vehicle body upon which the shock absorber is mounted, with the result that the shock absorber has a combined springing characteristic for increased dampening action. Such shock absorber construction is advantageous in that it is simple in structure and provides a space-saving feature in that the cap is positioned at one end of the shock absorber, adjacent to the vehicle body.
The secondary performance of the conventional shock absorber which takes place between the shock absorber and the vehicle body is functionally dependent on hydraulic pressure and resilient deformation of the rubber mount, the resiliency of the rubber mount being proportional to the amount of load acting thereon. The problem with such arrangement is that the springing characteristic of the rubber mount should be determined with respect to the maximum loading capacity of the vehicle. Thus, the rubber mount becomes relatively rigid when the vehicle is lightly loaded, resulting in discomfort to passengers of the vehicle.
Pneumatic cushioning utilizing gas pressure such as air pressure has been practiced in a variety of fields. Such pneumatic cushioning can provide a desired soft springing characteristic under a given amount of loading and stroke, but beyond such given amount the pneumatic cushioning causes the spring constant to rapidly become higher, thereby resulting in less comfort to the passengers when the vehicle is heavily loaded.
The present invention provides a hydraulic shock absorber for vehicles which eliminates the above-described difficulties and utilizes hydraulic pressure as well as the resiliency of a rubber mount, while also employing pneumatic cushioning.